106 SCIENCE PROGRESS 



III. The Synthesis of the Proteins. The Polypeptides 



Many theories have been advanced concerning the constitu- 

 tion of the proteins as to how the amino acids, the key-stones, 

 are combined together. The majority of the views regard the 

 amino acids as being bound together in an anhydride-like 

 manner in the form of acid amides. This view has been very 

 strongly supported by Hofmeister, and several experimenters 

 had already attempted to combine the amino acids together in 

 this manner. Thus, Schaal made the anhydride of aspartic 

 acid, which was further condensed by Grimaux and Schiff. 

 Schutzenberger condensed amino acids with urea, Lilienfeld 

 employed a mixture of amino acid esters, and Balbiano and 

 Frasciatta obtained a horny mass, an anhydride of glycine. 



Not, however, until Fischer commenced his systematic 

 researches upon the combination of the amino acids with one 

 another in 1901 was any real progress made. Since then the 

 enormous number and variety of products which have been 

 prepared by Fischer and his pupils have given us an actual 

 knowledge as to how the proteins are built up, and they show 

 us how much more complicated the proteins are than the fats 

 and carbohydrates, the other natural constituents of animal 

 and vegetable cells. The combinations of the amino acids 

 have been called by Fischer polypeptides, those containing 

 two, three, four, etc., acids being di-, tri-, tetra-peptides, etc. 

 They remind us in their nomenclature of monosaccharides, 

 dissacharides, polysaccharides, and of peptone, which Fischer 

 regards as a mixture of polypeptides. 



It was found by Curtius and Goebel many years ago that 

 the ethyl ester of glycine, when dissolved in water, lost two 

 molecules of alcohol, and was converted into diketopiperazine, 

 or, as it is now better called, glycine anhydride, 



NH. CH 2 .CO 



I ' I 



CO.CH...NH 



This substance formed the starting-point of E. Fischer's investi- 

 gations ; by boiling it with concentrated hydrochloric acid the 

 piperazine ring was split, and it gave the hydrochloride of 

 the base C 4 H 8 N 2 3 , thus 



NH.CH...CO 



I I + H,0 = H..N . CH..CO.NH . CH, . COOH 



CO.CH..NH 



